In recent years, there has been an increasing need for long term operation of a steam turbine in an extremely low load region. An example of the extremely low load operation is on-the-spot load operation for generating only on-the-spot power in a power plant.
In the extremely low load region, a low pressure downstream stage in the steam turbine does not cause any work, but conversely acts as a brake. Therefore, the operation in the extremely low load region results in generating heat in the low pressure downstream stage and increasing temperatures of blades in an exhaust chamber and a final stage of the steam turbine. In order to suppress the increases of these temperatures, a conventional steam turbine power generating facility operates exhaust chamber spray water of the steam turbine in a method as illustrated in FIG. 3.
FIG. 3 is a graph illustrating a conventional operation range of exhaust chamber spray water.
The horizontal axis in FIG. 3 indicates a load of the steam turbine (turbine load). The vertical axis in FIG. 3 indicates a temperature in the exhaust chamber of the steam turbine (exhaust chamber temperature). A region R1 indicates a region of operating the exhaust chamber spray water. A region R2 indicates a region of not operating the exhaust chamber spray water.
Regarding FIG. 3, in the case where the turbine load is larger than L1, the exhaust chamber spray water is operated when the exhaust chamber temperature is higher than T1, and the exhaust chamber spray water is not operated when the exhaust chamber temperature is lower than T1. On the other hand, when the turbine load is smaller than L1, the exhaust chamber spray water is operated at all times regardless of the exhaust chamber temperature. By doing so, in the extremely low load region, the exhaust chamber spray water is operated at all times, so that the increase in temperature of the blades of the exhaust chamber and the final stage of the steam turbine can be suppressed.
FIG. 4 is a schematic diagram illustrating a configuration of a conventional steam turbine power generating facility.
The steam turbine power generating facility in FIG. 4 includes a steam turbine 1, a generator 2, a main steam valve 3, a condenser 4, an actuation valve 5, an exhaust chamber spray 6 and an exhaust chamber cooling apparatus 7.
In FIG. 4, main steam from piping having the main steam valve 3 is introduced into the steam turbine 1, so that a rotor of the steam turbine 1 is rotated with the steam, the rotation of the rotor drives the generator 2, and the generator 2 generates power. The steam discharged from an exhaust chamber R of the steam turbine 1 is condensed by the condenser 4 to be changed back to water. The water is cooled by a cooling system downstream of the condenser 4. A part of the water cooled by the cooling system is given pressure by a pump and fed to the exhaust chamber spray 6 in the exhaust chamber R from piping having the actuation valve 5 to be released in the exhaust chamber R as spray.
The exhaust chamber cooling apparatus 7 in FIG. 4 includes an output measuring module 11, an output lower limit restricting module 12, an output setting value inputting module 13, a logical negation (NOT) module 14, an actuation valve controller 15, a temperature measuring module 21, a temperature upper limit restricting module 22, a temperature setting value inputting module 23 and a logical sum (AND) module 24.
The output measuring module 11 measures output of the generator 2 (generating-end output) and outputs a measurement value W of the generating-end output. The output lower limit restricting module 12 compares the measurement value W of the generating-end output with an output setting value WL that is set in the output setting value inputting module 13 and outputs a signal S1 containing the comparison result. The signal S1 is low when the measurement value W of the generating-end output is larger than the output setting value WL (W>WL), and is high when the measurement value W of the generating-end output is smaller than the output setting value WL (W<WL).
The temperature measuring module 21 measures a temperature in the exhaust chamber R of the steam turbine 1 (exhaust chamber temperature) and outputs a measurement value T of the exhaust chamber temperature. The temperature upper limit restricting module 22 compares the measurement value T of the exhaust chamber temperature with a temperature setting value TU that is set in the temperature setting value inputting module 23 and outputs a signal S2 containing the comparison result. The signal S2 is low when the measurement value T of the exhaust chamber temperature is smaller than the temperature setting value TU (T<TU), and is high when the measurement value T of the exhaust chamber temperature is larger than the temperature setting value TU (T>TU).
The NOT module 14 outputs the NOT value of the signal S1 as a signal S3. Therefore, the signal S3 is low when the measurement value W of the generating-end output is smaller than the output setting value WL (W<WL), and is high when the measurement value W of the generating-end output is larger than the output setting value WL (W>WL).
The AND module 24 outputs the AND value of the signal S2 and the signal S3 as a signal S4. Therefore, the signal S4 is high when the measurement value W of the generating-end output is larger than the output setting value WL and the measurement value T of the exhaust chamber temperature is larger than the temperature setting value TU (W>WL and T>TU). Otherwise, the signal S4 is low.
The actuation valve controller 15 controls the actuation valve 5 based on the signal S4 or S1 to control supply of spray water into the exhaust chamber R of the steam turbine 1. The exhaust chamber R is cooled with the spray water. For example, the actuation valve controller 15 is turned ON when the signal S4 or S1 is high, opens the actuation valve 5 at its full state, and thereby, operates the exhaust chamber spray water. Otherwise, the actuation valve controller 15 is turned OFF and fully shuts the actuation valve 5, so that the exhaust chamber spray water is not operated.
Accordingly, the actuation valve controller 15 operates the exhaust chamber spray water when the signal S4 is high, that is, when the measurement value W of the generating-end output is larger than the output setting value WL and the measurement value T of the exhaust chamber temperature is larger than the temperature setting value TU (W>WL and T>TU). This corresponds to the case where the turbine load is larger than L1 in FIG. 3.
Moreover, the actuation valve controller 15 operates the exhaust chamber spray water when the signal S1 is high, that is, when the measurement value W of the generating-end output is smaller than the output setting value WL (W<WL). This corresponds to the case where the turbine load is smaller than L1 in FIG. 3. As indicated by sign P, the signal S1 is supplied from the output lower limit restricting module 12 to the actuation valve controller 15.
In this way, the operation range of the exhaust chamber spray water illustrated in FIG. 3 can be realized by the steam turbine power generating facility in FIG. 4.
FIG. 5 is a graph illustrating an example of no-load operation that was performed in another conventional steam turbine power generating facility. It should be noted that the same reference numerals as those for the steam turbine power generating facility in FIG. 4 are used in the following description for convenience of explanation.
The horizontal axis in FIG. 5 indicates time. A curve C1 indicates the number of revolutions of the rotor of the steam turbine 1 (rotor rotational speed). A curve C2 indicates a pressure in the condenser 4 (condenser pressure). Sign S denotes an operation state of the exhaust chamber spray water in the exhaust chamber R of the steam turbine 1. A curve C3 indicates a temperature in the exhaust chamber R of the steam turbine 1 (exhaust chamber temperature). A curve C4 indicates a temperature of a nozzle (nozzle tip portion) in the final stage of the steam turbine 1. A curve C5 indicates a temperature of a nozzle diaphragm (nozzle tip portion) in the final stage of the steam turbine 1.
FIG. 6 is a cross-sectional view for explaining measurement positions of the temperatures shown in FIG. 5.
Sign L-0 denotes the nozzle in the final stage of the steam turbine 1. Sign A1 denotes a measurement position of the temperature of the curve C4. Sign A2 denotes a measurement position of the temperature of the curve C5.
Typically, if the steam in the exhaust chamber R is wet steam, latent heat of the moisture in the steam suppresses the exhaust chamber temperature at the saturation temperature. However, in no load, the condition in the exhaust chamber R is a dry condition. Therefore, in no load, the exhaust chamber temperature drastically elevates if the exhaust chamber spray water is not inputted to the exhaust chamber R.
This will be explained with reference to FIG. 5. The state of the steam turbine 1 during the period of time illustrated in FIG. 5 is a no-load operation state, and the exhaust chamber spray 6 is tentatively manually operated to be turned ON/OFF.
The steam turbine 1 is started at 10:30 and the rotor rotational speed C1 is elevating from 10:30. The condenser pressure C2 is approximately 7 inHga at 10:30.
Until the rotor rotational speed C1 becomes stable at 2500 rpm at 13:20, the exhaust chamber temperature C3 has elevated up to 270 degrees Fahrenheit (approximately 130° C.). The operation state S of the exhaust chamber spray water is partially manually switched to be ON at 13:20. By doing so, the exhaust chamber temperature C3 descends down to 160 degrees Fahrenheit (approximately 70° C.).
After that, the rotor rotational speed C1 is increased from 2500 rpm, and simultaneously, the condenser pressure C2 is reduced. The rotor rotational speed C1 has reached the rated rotational speed of 3600 rpm at 14:00. In this stage, the condenser pressure C2 is approximately 6.5 inHga.
The operation state S of the exhaust chamber spray water is switched to be OFF from 14:00 for several minutes. By doing so, the exhaust chamber temperature C3 drastically elevates again up to 270 degrees Fahrenheit (approximately 130° C.).
Upon switching the operation state S of the exhaust chamber spray water to be ON again, the exhaust chamber temperature C3 drastically descends down to 160 degrees Fahrenheit (approximately 70° C.).
After that, with the rotor rotational speed C1 maintained at the rated rotational speed of 3600 rpm, the condenser pressure C2 is gradually reduced. After the condenser pressure C2 has reached the rated pressure of 5.5 inHga, this pressure is maintained as the condenser pressure C2.
In this state, the operation state S of the exhaust chamber spray water is switched to be OFF again from 16:15 for several minutes. By doing so, the exhaust chamber temperature C3 drastically elevates again up to 250 degrees Fahrenheit (approximately 120° C.).
Upon switching the operation state S of the exhaust chamber spray water to be ON again, the exhaust chamber temperature C3 drastically descends down to 150 degrees Fahrenheit (approximately 65° C.).
During an OFF period from 16:15 for several minutes, the temperature C4 of the nozzle in the final stage has reached 430 degrees Fahrenheit (approximately 220° C.) and the temperature C4 of the nozzle diaphragm in the final stage has reached 445 degrees Fahrenheit (approximately 230° C.).
The followings are apparent from the aforementioned explanation.
1) As mentioned above, if the exhaust chamber R is in the wet state, the exhaust chamber temperature can be suppressed at the saturation temperature. However, the exhaust chamber R in no load is in the dry condition. Therefore, the exhaust chamber temperature drastically elevates if the exhaust chamber spray water is not inputted to the exhaust chamber R. This is apparent from the elevation of the exhaust chamber temperature during the OFF period around 14:00 and the elevation of the exhaust chamber temperature during the OFF period around 16:15.
2) When the exhaust chamber spray is operated, the exhaust chamber temperature becomes the saturation temperature at the condenser pressure. Therefore, the lower the condenser pressure is, the lower the exhaust chamber temperature becomes. This is apparent from the exhaust chamber temperature after the OFF period around 14:00 being 70° C. and the exhaust chamber temperature after the OFF period around 16:15 being 65° C.
3) The temperature of the nozzle tip portion in the final stage becomes an exceedingly higher temperature as compared with the exhaust chamber temperature. This is apparent from the curves C3, C4 and C5. This phenomenon arises also in the blade tip portion of the final stage. Hereafter, a mechanism thereof will be described.
FIG. 7 is a cross-sectional view illustrating a backward flow and a drift that arise in low load operation of the conventional steam turbine 1.
FIG. 7 illustrates a blade 1a and a nozzle 1b in the final stage of the steam turbine 1. Sign P1 denotes a tip portion of the blade 1a and sign P2 denotes a root portion of the blade 1a. In extremely low load operation of the steam turbine 1, an outlet flow of steam in the final stage contains a backward flow from the outlet side and a drift toward the tip in the radial direction. Sign H1 denotes a height of a backward flow region in the radial direction and sign H2 denotes a height of the blade la in the radial direction.
FIG. 8 is a graph illustrating a relation between the turbine load and the backward flow region in the conventional steam turbine 1.
The horizontal axis in FIG. 8 indicates the turbine load on the steam turbine 1. The vertical axis in FIG. 8 indicates a radial directional position from the root portion P2. FIG. 8 shows that the backward flow region becomes wider as the turbine load decreases more. Therefore, in extremely low load operation of the steam turbine 1, a wide backward flow region arises.
FIG. 9 is a graph illustrating relations between the turbine load and the blade tip temperature and exhaust chamber temperatures in the conventional steam turbine 1. The blade tip temperature is a temperature of the blade tip portion P1.
When the wide backward flow region arises in the final stage of the steam turbine 1, heat generated from the blade 1a is collected in the blade tip portion P1 and the blade tip temperature becomes higher than the temperature in another place of the blade 1a. Therefore, in extremely low load operation of the steam turbine 1, the blade tip temperature can be higher than the exhaust chamber temperature by 150° C. or more as illustrated in FIG. 9.
In this manner, in extremely low load operation, even when the exhaust chamber temperature is low, the blade tip temperature is high. Moreover, since the blade tip temperature suffers wide variation depending on the measurement position of the temperature, this is not proper for use as a value for control. Therefore, in the conventional extremely low load operation, the exhaust chamber spray water is designed so as to be operated at all times without the operation of the exhaust chamber spray water controlled based on the exhaust chamber temperature and the blade tip temperature.